The present invention relates to an optical body, a window member, a fitting, a solar shading device, and a building. More particularly, the present invention relates to an optical body for directionally reflecting incident light.
Recently, cases of coating a layer, which partly absorbs or reflects the sunlight, on architectural glasses for high-rise buildings and housings, vehicular window glasses, etc. have increased. Such a trend represents one of energy-saving measures with the view of preventing global warming, and it is intended to reduce a load of cooling equipment, which is increased with optical energy incoming from the sun, entering the indoor through windows, and raising the indoor temperature. The optical energy incoming with the sunlight is primarily provided in a visible range at wavelengths of 380 to 780 nm and in a near infrared range at wavelengths of 780 to 2100 nm. Because transmittance of light in the latter near infrared range through windows is unrelated to visibility of human eyes, the transmittance of the near infrared light is an important factor affecting the performance as a window that has high transparency and a high thermal shielding ability.
As methods for blocking the near infrared light while maintaining transparency in the visible range, there are a method of providing, on a window glass, a layer having a high reflectance in the near infrared range, and a method of providing, on a window glass, a layer having a high absorbance in the near infrared range.
With regards to the former method, various techniques using, as reflecting layers, an optical multilayer film, a metal-containing film, a transparent electroconductive film, etc. are already disclosed (see, e.g., International Publication No. 05/087680). However, those reflecting layers are formed on a flat window glass, and they can just specularly reflect the incident sunlight. Therefore, the light incoming from the sky and reflected specularly reaches other buildings and the ground in the outdoor where the light is absorbed and converted to heat, thus raising the ambient temperature. Accordingly, a local temperature rise occurs in the surroundings of a building in which all windows are coated with the above-mentioned type of reflecting layer. Such a local temperature rise causes the problems that, in urban areas, a heat island phenomenon is accelerated, and that the lawn grass does not grow only in areas irradiated with the reflected light.
As the latter method, various techniques using organic pigment layers are disclosed (see, e.g., Japanese Unexamined Patent Application Publication No. 06-299139, No. 09-316115, and No. 2001-89492). However, when the pigment layer is affixed to a window glass, light absorbed at the window surface is converted to heat and part of the heat is conducted as radiant heat to the indoor. This raises the problems that the shield ability of the pigment layer is insufficient, and that the glass may be cracked due to thermal stress. Further, there is another problem that the pigment layer is poor in weatherbility and is less convenient when used in high-rise buildings in which frequent replacement of the pigment layer is difficult.